Diesel combustion engines are widely used in heavy-duty trucks, stationary engines (e.g., agriculture engines, water pumps, etc.), and for power generation. They have better efficiency compared to gasoline internal combustion engines and offer better mileage in automotive applications. However, diesel engines tend to have higher nitrogen oxides (NOx) and particulate matter (PM) emissions, which are critical pollutants. With the advent of common rail injection systems and many performance-enhancing modifications, modern diesel engines have decreased their emissions, but still emit relatively high concentrations of particulate matter within a wide range of particle sizes. To meet the emission regulations, a number of diesel particulate filters (DPF) have been developed and implemented as viable devices to minimize diesel soot emission.
Most of the particles from diesel exhaust are less than 2.5 μm in diameter with a substantial fraction of particles being less than 100 nm in diameter. The diesel particulate filters are capable of capturing a substantial fraction of the exhaust particles and can be an effective means of reducing both the particulate mass and particulate number of emissions. However, the current DPFs are not very effective for capturing ultrafine (i.e., less than 100 nm) particles, which have been linked with increased morbidity and mortality. In addition, during the continuous operation of the filter, the captured particles continue to accumulate inside the DPF and cause the pressure in the exhaust system (called backpressure) to increase. Increased backpressure reduces fuel economy and reduces engine performance, thus creating the need for a regenerative or cleansing process. In all traditional DPFs, the regeneration is achieved by burning off the collected matter, which requires consumption of fuel and creates secondary aerosol emission, especially in the 10 to 30 nm size range. The particles produced during DPF regeneration are not captured and contribute ultrafine particles to air pollution.
There therefore exists a need for alternative emission control systems and methods that can reduce engine exhaust particulates.